The present invention relates to a support member for a prosthesis, particularly for a prosthesis to provide an artificial joint, the support member consisting of a tubular member for securing the prosthesis to bone tissue.
It is known permanently to reconstruct the extremities and other joints of a body such as a human body which are malformed either from birth, or due to disease or accident, in various ways.
One known technique involves the substitution of the components of a joint made from a biologically acceptable material such as metal or plastics material the material being inserted in a bore formed in the ends of the bone and being held in place by a cementing process. The conventional form of cement utilized is plastics material cement, based on polymers, which are capable of forming organic chemical monomers. These cements are prepolymerised in order to ensure sufficient plasticity to apply them. However, if the cements are to be finally cured, they need to be raised to a high reaction temperature and this, together with the side effects produced by the monomers, has a disadvantageous biological effect on the bone, killing the bone tissue. Thus, this technique, although it is satisfactory in the short term, is not suitable for long term use.
Prosthetic devices have already been satisfactorily manufactured from biologically compatible metal such as titanium and titanium alloys or vitallium.
Plastics materials have also been used to form the components of a prosthesis, although plastic prosthesis are normally only suitable for smaller joints, such as finger joints. The actual retention of the prosthesis device in the bone is a function of the cement itself, and it has been conventional to use methyl acrylic and polymethyl acrylic cements, or methyl metacrylicstyrene copolymers with or without the addition of barium sulphate. As mentioned, however, the bond thus obtained is not entirely satisfactory for the reasons outlined above.
Furthermore, a prosthesis has been proposed, intended for producing an artificial joint, having a member which can be inserted into a recess in the bone, this prosthesis comprising a tubular support member having a plurality of lateral openings disposed at spaced locations around the periphery of the support member and passing through the wall thereof, and also a prosthesis body locatable at least in part in said support member and means for securing the prosthesis body in place in the support body.
With such a prosthesis, the bone to be treated is prepared in conventional manner, and the tubular support member is then inserted in the hollow interior of the bone. A suitable cement of the kind mentioned above is introduced into the tubular support member so that it passes locally through the openings and only comes into contact with the bone at the location of these openings. The cement is cured, and the prosthesis body is positioned either prior to or during this curing and is secured in place in the tubular support member.
With such an arrangement, the only portion of the bone tissue which is in any way damaged is that portion which is touched by the cement. The cement serves to hold the tubular support member in position for a short time or moderate period of time. This is sufficient to allow the bone tissue to grow inwardly and anchor the remainder of the tubular support member in place. Thus, when the bond between the cement and the bone breaks down, as it will in due course, the bone tissue will hold the support member in place.
However, it has been found that the know prostheses do not provide satisfactorily for the growth of bone tissue around the support member. It has also proved difficult to apply suitable and necessary therapeutic aids to the support member, such as anticoagulants, chemotherapeutic aids, substances to expand the blood vessels and microbicides.